Hardening or treatment of steel, iron, &amp;c.



UNITED STATES PATENT OFFICE.

ADOLPH W. MACHLET, OF ELIZABETH, NEW JERSEY.

HARDENING OR TREATMENT OF STEEL; IRON, &c.

No Drawing.

T 0 all whom it may concern:

Be it known that I, ADOLPH W. MAcHn-ET, a citizen of the United States,residing in Elizabeth, in the county of Union and State of New Jersey,have invented certain new and useful Improvements in the Hardening orTreatment of Steel, Iron, &c., of which the following is aspecification.

This invention relates to treating iron and steel articles, as well asarticles of some other metals, in a manner to produce upon the articlesa coating, skin, shell or finish, or to affect the nature of thearticles throughout, as the case may be; that is, to harden andotherwise modify the articles, either exteriorly or throughout.

In the preferred manner of treating lowcarbon steel articles accordingto my invention or discovery, they are placed in a retort such as shownin U. S. Letters Patent No. 822,460 of June 5, 1906, 'or No. 884.181, ofApril 7, 1908,01 No. 961,305, of June 14, 1910. and the retort is heatedto a carburizing heat, while a current of ammonia flows slowly throughthe retort. the ammonia having first been charged with naphtha, as setforth in said Patent No. 961,305. Or the ammonia may be in the form ofbubbles taken up .by hydrocarbon gas passing through the ammonia, as setforth in said Patent No. 884,181. steel is carburized as deeply as maybe desired. This operation may continue from a few minutes to severalhours, according to the depth of carburization desired, the quality ofthe material, etc. Then I shut off the naphtha," and cause the ammoniaalone to flow slowly through the retort, for half an hour or more, whilethe said heat of the retort is maintained. If anammonia-andnaphtha-mixing apparatus is used, a bypass may be connectedover from the ammonia supply to the retort-supplying pipe, said bypassto be provided with a valve to close the same when desired. By thismeans,

the ammonia may be made to flow either through the naphtha, as whencarburizing the metal, or directly through the bypass to the retort,without taking up any naphtha. One effect of the ammonia treatment is torid the articles of any surplus deposit of carbon thereon. After asuificient'duration of the ammonia treatment subsequent to suchcarburization or case-hardening, I close the vent of the retort, andpermit the retort to cool while the same remains filled withSpecification of Letters Patent. Application ma m 12, 1907. Serial No.383,422.

.By this means, the low-carbon Patented Apr. 14., 1914.

ammonia and contains the steel articles. This prevents accessof air oroxygen to the articles; although the invention is not limited to thisparticular method of preventing oxidization of the heated article. Thearticles when \examined after cooling, are found to be. not onlycase-hardened as set forth in 'said Letters Patent, but also to beprovided with an integral skin, casing, shell or coating, which whenunpolished has a silvery color, and is very compact and closegrained andhard; and is capable of taking a very high polish closely resemblingpolished silver. It is so hard that it is diflicult to polish, anddifiicult or impossible to cut with an ordinary machinists file; and insome cases it may be sufliciently hard to scratch glass. This coating isextremely reluctant to tarnish, corrode, or rust, or to oxidize; andunder ordinary conditions may be regarded as practically proof againstrust, as for instance in indoor use, or where it is not unduly exposedto the elements. Articles made according to my invention have beensubmitted to many tests at the same time with common steel untreatedscrews and other articles; and while the latter rusted in the expectedmanner, the former showed no signs of rust or even oxidization. Theinvention is therefore of, value in treating parts of machinesandinstruments, to prevent their rusting, and give them an attractivefinish, andavoid the necessity of nickeling, silvering or otherwiseplating or finishing them; while the hardness of the I casing renders itdesirable for wearing parts, cutlery, and in numerous other arts. Thissilvery casing is much harder than iron or low-carbon steel. It isbrittle, but owing to the qualities of the case-hardened shell whichbacks it up, and to the presence of the softer steel beneath said shell,the brittleness is found unobject-ionable in practice. Said silverycasing is capable of beingstill further hardened by heating andquenching. It is magnetic. It is difficult or impossible to anneal saidsilvery casing by ordinary methods. a granular or granitic fracture ofvery fine grain. It may be acted upon by vitriol or muriatic acid inmuch the same manner as iron, but is very reluctant toyield to saidacids. When red hot, said silvery casing is harder than tool steel atthe same heat, and in many instances is too hard to bescratched with afile. If exposed to air when at a red heat, it oxidizes more rapidlythan tool steel or iron at the same heat. It will be un derstood thatthe articles may be carburized throughout, if desired, before beingsubjected to the final heating in pure ammonia, to form the coating.Substantially similar results may be obtained by similar treatment ofSwedish iron or pure. iron, or wrought iron, etc.

In treating gray cast iron, such as commonly employed for machine framesand small machine castings, and in which there is a relatively largeamount of carbon as compared with low-carbon steel, I pass the ammoniathrough kerosene or heavy oil instead of through naphtha, so that the ammonia will take up only a little hydrocarbon on its passage into theheating retort; and I continue the heating of the cast iron five hoursor more in the atmosphere of ammonia and hydrocarbon; finishing thetreatment, however, with the half hour of the current of pure ammonia,and permitting the iron articles to cool in a bath of ammonia, as beforeexplained. This produces upon the cast iron a-hardened integral shell orcasing, having substantially the same characteristics as already notedwith regard to low-carbon steel articles treated according to myinvention. If the cast iron, however, is first decarburized or mademalleable, it may be treated in the same 'way as the low-carbon steelarticles, with substantially the same results as before noted. Withhigh-carbon or tool steel, the process should be substantially the sameaswith gray cast iron articles. The low-carbon steel articles, aftercarburization, may be subjected to the heat-andammonia treatment, asbefore, and then after cooling, they may be re-heated and quenched, andsubsequently again heated and quenched; and this "may be again repeated;each r'e-heating and quenching serving to improve the hardness andtenacity of the case-hardened or carburized portions of the articles.The re-heating in each instance should be done in a carbonaceousatmosphere. So far as the repeated re-heating and quenching isconcerned, the ammonia finishing, treatment may be omitted, as there-heating and quenching improves articles case-hardened, even if theyare not finished with the herein described coating. There should be noexcess of carbon present in the retort.

By subjecting low-carbon steel to the heat treatment as aforesaid forseveral hours in an atmosphere of ammonia which has been passed throughkerosene or heavy oil instead of naphtha (the ammonia, it will beunderstood, takes up less carbon or hydrocarbon from the kerosene thanit does from naphtha), the entire mass of the steel becomes afi'ectedand brittle, and hardened, but not so hard as the skilletcrustheretofore described. This metal is magnetic, and possesses many ofthe properties of said skin or shell. Now, if it is desired to form onthis present metal a shell or crust such as hereinbefore described, itcan be done in the hereinbefore' described manner, viz., by subjectingthe heated metal to the action of ammonia alone, for half an hour ormore. The crust is exceedingly fine-grained and compact, in comparisonwith the'body of the metallic article, besides being harder than saidbody. This coating or crust is only a few thousandths of an inch inthickness, and after repeated attempts I have been unable to make itmuch if any thicker; and I suppose that owing to the exceedingly compactnature of the crust, the ammonia (or ammonium or ammonium and carbon) inthe retort is prevented from gaining access through the crust to theinterior of said body, so that a crust of this character and of greatthickness has; not yet been formed, even after hours of exposure to thetreatment. The crust, it has been seen, can be formed either on the bodyof the metal, or on case-hardened steel or iron, or directly onlow-carbon steel or high-carbon steel or cast ray) iron or on malleableiron or on wrong t iron or on high-carbon steelin fact on any metal ofwhich iron isthe main component.

Variations in the processes and metals may be resorted to within thescope of the invention. In carburizing previousito incrusting the metal,a gas consisting only of hydrogen and carbon may beemployed to flowthrough the retort; that is to say, the nitrogen component of ammoniamay be omitted when case-hardening articles, whether or not they are tobe subsequently incrusted with the new hard silvery metal hereindescribed.

Not only metals of the iron class, but also other metals, as forinstance nickel, may be subjected to the herein described treatment toincrust the same in like manner; and it will be understood that in manycases, as for instance in incrusting small articles in bulk, it ispreferable to rotate the retort during the operation of heating thearticles in an atmosphere of the described gases, so as to agitate thearticles and expose them all over to the action of the gas, and causeevery side of each article to come uppermost in turn. I

also recommend, instead of passing ammonia through carbon, to use pureammonia to which a lenum of hydrogen has been added (NH p us H); thisgas to be used for either affecting the body of the article, or simplyfor incrusting the same with the hard substance described.

Having thus described my invention, I claim:

1. The process of treating iron or steel, comprising the steps ofheating the metal at least to about red heat in an atmosphere of ammoniaand hydro-carbon, and then in an atmosphere of ammonia.

2. The process of treating iron or steel articles, comprising the stepsof heating them at least to about redness in an atmosphere of ammoniawhich has been passed or filtered through kerosene, and then in anatmosphere of ammonia alone.

3. The process of passing ammonia through a heavy oil and introducing itinto a heated retort. containing iron or steel articles, and thencausing a current of ammonia alone to flow through the retort over theheated articles.

4. The process of treating low-carbon steel or iron comprising the stepsof heating it in an atmosphere of ammonia which has been passed throughkerosene, until the article throughout is converted into a hard,brittle, silvery substance and then continuing the action with ammoniaalone.

5. The process of carburizing iron or steel articles, and then exposingthem to ammonia to rid the articles of the surplus deposit of purecarbon upon their surfaces, while the articles are still red hot orabove red heatfrom the carburizing operation, and then cooling themwithout access of air or oxygen.

6. The process of treating iron or steel, comprising the steps ofheating the metal to or about red heat in an atmosphere of ammonia andhydro-carbon, and then in an atmosphere of ammonia, then permitting thearticles to cool, then reheating and quenching the articles, and thenagain heating and quenching them.

7. The process of treating iron or steel comprising the steps of-heatingthe metal to or about red heat in an atmosphere of ammonia andhydro-carbon, and then in an atmosphere of ammonia, then permitting thearticles to cool, then reheating the articles in a carbonaceousatmosphere and quenching them, and then again heating and quenchingthem.

8. The process of passing ammonia through kerosene and introducing it ina heated retort containing metal articles, to cause the latter tocombine with the constituents of the ammonia and kerosene, and thenintroducing ammonia alone into the retort while the articles are stillheated.

9. The process of passing ammonia through kerosene and introducing it ina heated retort containing metal articles to cause the latter to combinewith the con stituents of the ammonia. and kerosene, then introducingammonia alone into the retort while the articles are still heated, andpermitting the articles to cool without exposure to air.

10. The process of treating iron or steel articles by exposing them whenheated to an atmosphere of carburizing gas and ammonia to produce ashell or coat thereon, and then exposing them while still heated to anatmosphere of ammonia alone, and then permitting the articles to cool inan atmosphere devoid of oxygen.

PHILIP C. OSTERMAN, SAMUEL R. OGDEN.

